System and method for detecting failures and re-routing connections in a communication network

ABSTRACT

A method of re-establishing a connection for a communication link is provided. The link has first and second portions, having the first portion in a first communication network, the second in a second communication network and an interface connecting first portion to the portion. The first communication network has a first communication protocol and a first OAM protocol to monitor integrity of the first portion. Similarly, the second communication network has a second communication protocol and a second OAM protocol. The method utilizes the second OAM protocol to detect a failure in the second portion. Upon detection of the failure, an alternate route for the second portion in the second communication network is identified, where the alternate route is able to complete the second portion of the communication link from the interface. For the communication link, at the interface the second portion is replaced with the alternate route.

This application is a continuation of U.S. patent application Ser. No.10/015,573, filed Dec. 17, 2001 now U.S. Pat. No. 7,164,652, andincorporated herein by reference.

FIELD OF ART

The invention relates to digital communication systems and morespecifically to an implementation of a network node capable of providingasynchronous transfer mode (ATM) traffic to multi-protocol labelswitching (MPLS) platform.

BACKGROUND OF INVENTION

MPLS is quickly gaining support in the communication industry as ahigh-speed core of many communication networks. Networks are beingdeveloped and deployed which interface ATM networks with MPLS networks.

There is a need for a system which can utilize aspects of MPLS OAM in anATM network, when an MPLS network is used as part of the ATM network.

SUMMARY OF INVENTION

In a first aspect, a method of re-establishing a connection for acommunication link is provided. The communication link has a firstportion in a first communication network, a second portion in a secondcommunication network and an interface connecting the first portion tothe portion. The first communication network has a first communicationprotocol and a first OAM protocol adapted to monitor integrity of thefirst portion; the second communication network has a secondcommunication protocol and a second OAM protocol adapted to monitorintegrity of the second portion. The method utilizes the second OAMprotocol to detect a failure in the second portion. Upon detection ofthe failure, the method identifies an alternate route for the secondportion in the second communication network, the alternate route beingable to complete the second portion of the communication link from theinterface. For the communication link, at the interface the methodreplaces the second portion with the alternate route.

The method may have the first communication network as an ATM network,the first OAM protocol as one of PNNI and ATM OAM, the secondcommunication network as a MPLS network and the second OAM protocol asMPLS OAM.

The method may perform identification of an alternate route for thesecond portion in the second communication network at the interface.

The method may utilize the second OAM protocol to detect a failure inthe second portion by monitoring the second portion for receipt offrames containing MPLS OAM information and debouncing the frames.

The method may identify an alternate route for the second portion in thesecond communication network by maintaining and accessing a list ofalternate routes for the second portion is maintained to identify thealternate route.

The method may have the first OAM protocol adapted to detect failures inthe second portion.

The method may utilize the second OAM protocol to detect clearance ofthe failure in the second portion. Upon detection of the clearance ofthe failure, for the communication link, the method replaces thealternate route with the second portion at the interface.

In a second aspect, a network node is provided. The node is associatedwith a first communication network and a second communication network.The node processes communications for a communication link. Thecommunication link has a first portion in the first communicationnetwork, a second portion in the second communication network and aninterface between the first portion and the second portion at thenetwork node. The first communication network has a first communicationprotocol and a first OAM protocol adapted to monitor integrity of thefirst portion; the second communication network has a secondcommunication protocol and a second OAM protocol adapted to monitorintegrity of the second portion. The node has a first module adapted todetect a failure in the second portion utilizing the second OAMprotocol, a second module adapted to receive an indication of thefailure and upon receipt of the indication, to identify an alternateroute for the second portion in the second communication network, thealternate route being able to complete the second portion of thecommunication link from the interface and a third module adapted toreceive an indication of the alternate route and to replace the secondportion with the alternate route for the communication link.

The node may have the first communication network as an ATM network, thefirst OAM protocol as one of PNNI and ATM OAM, the second communicationnetwork as a MPLS network and the second OAM protocol as MPLS OAM.

The node may have the first module utilizing the second OAM protocol todetect the failure in the second portion by monitoring the secondportion for receipt of frames containing MPLS OAM information and thefirst module debouncing the frames.

The node may have the second module further comprising a list ofalternate routes for the second portion to identify the alternate route.

The node may have the first module adapted to use the second OAMprotocol to detect clearance of the failure in the second portion andthe third module adapted to replace the alternate route with the secondportion for the communication link upon detection of the clearance ofthe failure.

In other aspects, the invention provides various combinations andsubsets of the aspects described above.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other aspects of the invention will become moreapparent from the following description of specific embodiments thereofand the accompanying drawings which illustrate, by way of example only,the principles of the invention. In the drawings, where like elementsfeature like reference numerals which may bear unique alphabeticalsuffixes in order to identify specific instantiations of like elements):

FIG. 1 is a block diagram of a prior art ATM communication network knownin the art with a failed link between two nodes therein;

FIG. 2 is a block diagram of an ATM network incorporating therein a MPLSnetwork according to an embodiment of the invention with a failed tunnellink between two MPLS nodes in the MPLS network;

FIG. 3 is a block diagram of two ATM cells and an equivalent MPLS framewhich are utilized by a node in FIG. 2 which embodies the invention;

FIG. 4 is a block diagram of a tunnel link connecting two MPLS nodes inthe MPLS network of FIG. 2;

FIG. 5 is a flow chart of an algorithm used to establish the tunnel linkof FIG. 3;

FIG. 6 is a diagram of various cases of OAM frames sent and monitoredassociated with the tunnel link of FIG. 4;

FIG. 7 is a block diagram of elements of a node embodying the inventioninterfacing the ATM network with the MPLS network of FIG. 2; and

FIG. 8 is a block diagram of a MPLS OAM state machine present in thenode of FIG. 7.

DETAILED DESCRIPTION OF EMBODIMENTS

The description which follows, and the embodiments therein, are providedby way of illustrating an example, or examples, of particularembodiments of principles of the present invention. These examples areprovided for the purpose of explanation, and not limitations, of thoseprinciples. In the description, which follows, like elements are markedthroughout the specification and the drawings with the same respectivereference numerals.

Referring to FIG. 1, prior art system 100 is shown, comprising an ATMnetwork whose general configuration is known in the art. Therein,network 102 comprises an interconnected number ATM switches 104connected by communication links 106 which can each carry ATM trafficthereon. At the edge of network 102, ATM edge switch 108 provides aconnection for Customer Premise Equipment (CPE) 110 to network 102.Similarly, at another edge of network 102, ATM edge switch 112 providesa link for CPE 114 to network cloud 102. It will be appreciated that ATMedge switch 108 may also have a connection to another ATM network 116.ATM edge switch 108 is connected to elements in network 102 via link118. Similarly, ATM edge switch 112 is connected to elements in network102 via link 120.

ATM edges switches have the ability to detect and reroute aroundfailures in network cloud 102, using known PNNI signalling or ATM OAMprotocols. When exemplary communications are sent from CPE 110 to CPE114 a PNNI signalling link first is established from ATM edge switch 108to ATM edge switch 112 through ATM switches 104. For example, initially,routing path 122 traversing ATM switches 104A, 104B and 104C isestablished. When the path 122 is available and a failure of an elementof an element therein occurs, for example, a failure in link 106connecting ATM switch 104B to ATM switch 104C, PNNI can be used tore-establish a connection along an alternate path.

Meanwhile, the embodiment provides a system and method for a node havinga connection to an ATM network and a connection to a MPLS network todetect and reroute around failures in established paths detected in theMPLS network utilizing MPLS OAM. Further detail on the embodimentutilizing a MPLS network is provided.

Referring to FIG. 2, system 200 is shown which includes a switchincorporating an embodiment. Therein, MPLS network 202 comprises MPLSswitches 204 which are linked via communication links 206. At one edgeof network 202, ATM/MPLS switch 208 provides and interface for ATMdevices such as CPE 210 to network 202. At another edge of network 202,ATM/MPLS switch 212 provides an interface point for an ATM device suchas CPE 214. ATM/MPLS switch 208 has a link to another ATM network 216.ATM/MPLS switch 208 communicates with MPLS switches in network 202 viacommunication link 218. Similarly, ATM/MPLS switch 212 communicates withMPLS switch 204C via communication link 220. It will be appreciated thatnetwork 202 may have other connections to other networks.

In order to provide quality of service (QoS) standards, for example likethose in an ATM network, for communications processed through MPLSnetwork 202, the MPLS switches 208 utilize MPLS signalling to establishdedicated and preset routing paths for traffic carried within MPLSnetwork 202. The routing paths are known to all elements in network 202.For example, if CPE 210 is in communications with CPE 214, after data istransmitted from CPE 210 to ATM/MPLS switch 208, the data is sentthrough MPLS network 202 using Label Switched Path (“LSP”) 222 betweenATM/MPLS switch 208 and ATM/MPLS switch 212. At switch 212, the data isforwarded to CPE 214. LSP 222 can also carry data from switch 212 toswitch 208. A LSP may also be referred to as a routing path.

Another requirement for QoS standards mandates that redundant MPLSrouting paths must be provided. In the event of a failure of a componentin MPLS routing path 222, for example, a failure in communication link206 connecting MPLS switch 204B to MPLS switch 204C, the failure has tobe detected and traffic has to be rerouted to an alternate MPLS routingpath, such as alternate MPLS routing path 224. Further detail on themechanism for monitoring and routing MPLS routing paths is providedbelow.

Accordingly, switch 208 is an embodiment providing a handshaking pointbetween ATM and MPLS networks allowing routing information from eachtype of network to be provided and used by the other network inmaintaining communication links. It will appreciated that switch 208 mayalso be referred to as a node, network element, routing switch or otherterms known in the art.

Referring to FIG. 3, aspects of the conversion of ATM cells receivedfrom CPE 210 by ATM/MPLS switch 208 to MPLS frames, and vice versa areshown. It will be appreciated that, as ATM/MPLS switch 208 is notionallyat edge of an ATM network and an MPLS network, ATM/MPLS switch 208 musttranslate ATM cells to MPLS frames and vice versa. ATM data is eitherencapsulated into cells or frames. Exemplary ATM cell 300 comprises 48bytes of data in data field 302 and five bytes of header data in headerfield 304. The header field includes data relating to error checkingdestination information. Frequently, ATM cells 300 are used to encodevoice calls in AAL 1/2/5 signalling parameters. ATM frames are used totransmit larger amounts of data. Exemplary ATM frame 306 comprises datafield 308 which may have 65 Kbytes of data. Header field 312 iscomparable to header field 304 for ATM cell 304. MPLS frame comprisesdata field 314, header field 316, first label field 318 and second labelfield 320.

When converting an ATM cell or frame to an MPLS frame, the respectiveATM data field (either data field 302 or 308) is inserted into MPLS datafield 314. Similarly, the contents of the respective ATM cell or frameheader fields (either header field 304 or header field 310) is insertedinto MPLS header field 316. First label field 318 and second label field320 are used to identify the routing information for MPLS frame 312through MPLS network 202. First label field 318 contains identificationinformation relating to the MPLS routing path for the MPLS frame. Forexample this first label field 318 may contain information relating tothe routing path relating to MPLS routing path 222. Second label field320 contains connection information relating to the particular internalATM connection which may be used by nodes 208 and 212 for routing theATM path. As the tunnels are known, each node in network 202 can examinethe contents of first label field 318 and direct the frame to theappropriate node in the network 202.

Referring to FIGS. 4 and 5, a description of the establishment andcontents of MPLS routing paths 206, 218 and 220 is provided. In theembodiment, MPLS routing paths 206, 220 and 218 are physically embodiedin separate fibre optic cables each carrying uni-directional data eitherto or from an MPLS switch 204 or ATM/MPLS switch 208. Using the exampleof MPLS routing path 218, downstream communications from ATM/MPLS switch208 to MPLS switch 204A are carried on a separate fibre connectionidentified as label switched path (LSP) 400. Similarly, communicationscarried from MPLS switch 204A to ATM/MPLS switch 208 are carried LSP402. It will be appreciated that LSP 400 and LSP 402 may be connected tothe same physical port on switch 208 which may be collectively groupedinto an MPLS tunnel constituting MPLS routing path 218. It will beappreciated that the term “tunnel” is interchangeable with the term“MPLS routing path”. A PNNI trunk group is created to associate LSP 400with LSP 402. The PNNI trunk group may be one of many trunk groupsassociated with a physical port on switch 208 that interfaces to MPLSnetwork 202. The trunk group also allows connection admission control(CAC) and ATM signalling of ATM connections over the tunnel using PNNIsignalling protocols.

Referring to FIG. 5, algorithm 500 is shown which is used establish,configure and monitor a tunnel, such as MPLS routing paths 222 and 224.First, at step 502, one LSP is created per direction between the sourceand destination MPLS switch nodes. In the embodiment, the source MPLSnode may be ATM/MPLS switch 208 and the destination MPLS switch may beATM/MPLS switch 212. Next at step 504, the two respective LSPs arecombined to create a tunnel. For the network shown in FIG. 2, the tunnelmay be MPLS routing path 222. Next at step 506, the PNNI signalling linkassociated with the ATM data is connected to the tunnel. Next at step508, the PNNI routing link associated with the ATM data is connected tothe tunnel. Finally, at step 510, tunnel monitoring is enabled. At thispoint, tunnel 222 provides a communication link between ATM/MPLS edgeswitch 208 to ATM/MPLS switch 212. The PNNI signalling and routing linksin the tunnel enable the embodiment to use PNNI signalling protocols todetect and react to any signalling failures in tunnel 222. However, asdescribed below, the embodiment utilizes MPLS OAM signalling protocolsinstead of PNNI protocols as MPLS signalling protocols provide improvedresponse times.

It will be appreciated that for alternate tunnel 224, algorithm 500 maybe repeated to establish an alternate routing path for ATM/MPLS switch208 to ATM/MPLS switch 212.

Referring to FIG. 4, LSP 400 and 402 may each carry PNNI signalling linkpackets, PNNI routing link data packets and specialized MPLS operation,administration and maintenance (OAM) frames. The MPLS OAM frames followITU Y.17 MPLS standards, which are incorporated herein by reference.There are three types of MPLS OAM frames used by the embodiment:

1) Connectivity verification (CV) frames;

2) Backward defect indicator (BDI) frames; and

3) Forward defect indicator (FDI) frames.

The type of MPLS OAM frame sent within an LSP is identified via theheader information and the second label field 320 in an MPLS frame. Thefirst label field 318 contains the tunnel identification informationrelated to the OAM destination. Presently, in the embodiment, a MPLS OAMframe is identified with a value defined by the MPLS standards bodies.Currently, the value is “5”. This value is placed in second label field320. The contents of the data field identify the type of MPLS OAM frame.

Referring to FIG. 6, a description of the ITU Y.17 OAM signallingprotocol used in the embodiment is provided by referring to tunnel 222between ATM/MPLS switch 208 and ATM/MPLS switch 212. The OAM signallingprotocol generally operates as follows: at an upstream switch, an OAMframe is generated and is transmitted in its associated LSP to adownstream switch. At the downstream switch the OAM frame is receivedand is analysed. Depending on the results of the analysis, thedownstream switch generates a response OAM frame which is transmittedupstream to the originating switch along its associated LSP. At theoriginating switch, the response OAM frame is received and analysed.Depending on the state of either LSP or either switch, the ultimateresponse message will indicate to the originating switch the status ofthe entire tunnel.

There are four signalling OAM cases generated depending on the status ofLSP 400, LSP 402, switch 212 and downstream components beyond switch212. To illustrate these signalling aspects in the embodiment, upstreamswitch is ATM/MPLS switch 208, downstream switch is ATM/MPLS switch 212,the originating frame module is transmit module 602, the receivingmodule is monitoring module 604, the reply transmit module is module 606and the receiving reply module is monitoring module 608.

Case A at 600 illustrates a tunnel 222 with no transmission problems inthe noted elements. At switch 208, at step one, transmit modules 602generates a CV frame and transmits it on LSP 400. At switch 212 at steptwo, the CV frame is received by the monitoring module 604. At stepthree, the monitoring module acknowledges receipt of the CV frame. Atstep four, the response CV frame is received at switch 208 at module608. Switch 208 can determine that tunnel 222 is fully operational bythe receipt of the response CV frame. CV frames are generated by CVtransmit module 602 and module 608 every one second according to ITUY.17 standards. Accordingly, after a certain transmission and frameprocessing delay, when tunnel 222 and its downstream components whichaffect tunnel 222 are fully operational, the response CV frames receivedby 208 should arrive approximately once every second. It will beappreciated that other time intervals could be used for transmitting CVframes.

In Case B at 610, it is presumed that there is a failure in LSP 400. Atstep one, CV transmitter module 602 generates and transmits its CV frameonto LSP 400. At step two, it will not be received by monitor 604 atswitch 212 due to the failure in LSP 400. Accordingly at step three, CVresponse transmitter generates a response BDI frame which indicates thata failure has occurred in the transmission link backward of switch 212as switch 212 did not receive the CV frame. The BDI frame is transmittedon LDP 402 and at step four it is received at switch 208 by CV/BDI/FDImonitor module 608. Switch 208 then can determine that the tunnel 222 isnot fully operational and can cause a traffic switch to an alternatetunnel.

In Case C at 612 it is presumed that there is a failure in both LDP 400and LDP 402. Accordingly, as with Case B, steps one, two and three areidentical. However, at step four switch 208 will not receive the BDIframe. Accordingly, switch 208 will recognize the absence of a responseto the originally transmitted CV frame and will, again, switch from thecurrently active tunnel 222 to an alternate tunnel.

Case D (not shown in FIG. 6) is a variation Case A. In a normalsituation if tunnel 222 is fully operational, switch 208 and switch 212will be able to transmit and receive CV frames therebetween. However, ifswitch 212 has an indication that downstream to it, there is a furtherfailure which affects tunnel 222, CV/BDI/FDI response module 606generates a FDI frame, which indicates that downstream of switch 212there is a forward integrity problem associated with tunnel 222. The FDIframe is transmitted from switch 212 to switch 208 via LDP 402. The FDIframe is received by CV/BDI/FDI frame monitor 608. Switch 208 can thenrecognize the fault downstream of tunnel 222 and can switch to analternate tunnel as necessary.

Additionally, a signal debounce mechanism is provided. As discussedearlier, switch 208 generates and inserts CV frames at one secondintervals. In the embodiment, a failure is noted by any receiving moduleonly after three consecutive frames either are not received or indicatethat there is a problem with the link (either through a BDI or FDIindication) to eliminate spurious error signals.

Referring to FIG. 7, details of switch 208 illustrating handshakingbetween MPLS OAM modules and PNNI signalling modules are provided.Switch 208 comprises ATM processing section 700 and MPLS processingsection 702. ATM section 700 comprises connection maintenance module 704and PNNI signalling module 706. ATM section 700 may reside in a centralcontrol module of switch 108. MPLS processing section 702 comprises CVframe generator and transmitter 603 and CV/BDI/FDI monitor 608, MPLSconnection control module 708, and MPLS OAM state machine 710. CVtransmitter module 602 and CV/BDI/FDI monitor 608 connect to physicalport 712 which connects to tunnel 218 and operate as described earlier.LSP management module 714 provides an interface for modules in the ATMprocessing section 700 and the MPLS processing section 702. MPLSprocessing section 702 may reside on a line card in switch 208. Theremay be several line cards in switch 108 having MPLS processing section702.

For MPLS functionality, MPLS OAM frames are generated by CV transmittermodule 602 and sent on tunnel 218. MPLS response frames are received byCV/BDI/FDI monitor 608 from tunnel 218. Thereafter, module 608 notifiesOAM state machine 710 of the OAM frame. OAM state machine 710 receivesthe OAM frames and determines whether the associated LSP tunnel is in aCV, BDI or FDI state.

Referring to FIGS. 7 and 8, OAM state machine 710 has three states:Unknown state 802, OK state 804 and Defect state 806. Uponinitialization, OAM state machine 710 starts in Unknown state 802.

State machine 710 will transition from Unknown state 802 to OK state 804if connectivity verification of the tunnel is successful. Connectivityverification may be successful upon receipt of a consecutive number ofCV packets. State machine 710 will transition from Unknown state 802 toDefect state 806 if connectivity verification fails or if a BDI or FDIpacket is received. In performing connectivity verification, CV packetsshould be received by OAM state machine 710 periodically, about onceevery second. However, after a period of time has elapsed withoutreceiving a CV packet, OAM state machine 710 moves to Defect state 806.In the embodiment, the LSP tunnel is in a CV failure state if CV packetsare not received in a window of approximately three seconds. Wheninitially in Unknown state 802 and state machine 710 receives either aBDI packet or an FDI, state machine 710 moves to Defect state 806.

While in Defect state 806, the defect can be cleared. If the defect wascaused by an absence of a CV packet, then the defect is cleared if statemachine 710 receives a series of consecutive CV packets. The number ofpackets may be configurable. If the defect was caused by the receipt ofeither a BDI or an FDI packet, then the defect may be cleared if statemachine does not receive a further BDI (or FDI) packet within a definedperiod of time. The defined period of time may be varied by the statemachine 710. Upon the clearing of a defect, state machine 710 moves toOK state 804.

In OK state 804, transitions are made to Defect state 806 upon theabsence of receipt of a number of CV packets or the receipt of either aBDI or FDI packet, as described above.

Referring back to FIG. 7, when a defect has not been cleared, OAM statemachine 710 signals the status of the tunnel 218 to LSP managementmodule 714 via generating and enqueing a Change of State entry 716 ofChange FIFO 718. The entry 716 contains information about thedestination LSP and MPLS OAM status information, i.e. informationrelating to the status of the CV, BDI and FDI frames. LSP managementmodule 714 periodically monitors FIFO 718 for new entries. Upondetection of a new entry therein, LSP management module 714 identifieswhich LSP failed and signals ATM signalling module 706 with a messageidentifying that there is a “link down” for the LSP.

ATM signalling module 706 manages ATM signal connections and processmessages indicating the availability of tunnels to contain ATMconnections, such as any “link down” messages from LSP management module714.

Signalling module 706 is associated with PNNI routing module 706A andPNNI signalling module 706B. PNNI routing module 706A has access totables and databases for all routing paths known to switch 108,including paths through network 202, which as such include paths 222 and224. PNNI signalling module 706B manages messaging to establish andclear connections. When a “link down” message is received, routingmodule 706A determines an alternate path to the failed link. Oncerouting module 706A decides upon the alternate path, it advisessignalling module 706B of the new routing change. Signalling module 706Bsends a message to connection maintenance module 704 with the newsignalling information. This new signalling information can be used whenrouting ATM traffic from CPE 210. Signalling module 706B also notifiesMPLS connection control module 708 of the new PNNI information.Accordingly, signalling module 706B can signal a call from node 208 tonode 212 using an ATM signalling protocol (e.g. PNNI). During thisexchange, the values for second label 320 are negotiated using PNNI.

The signal received by connection control module 708 notifies it to teardown the connection for the failed tunnel and establish a new MPLS routeover the alternate tunnel. For example, referring to FIG. 2, upon afailure of path 222, alternate path 224 may be selected. Routinginformation about the new path is also provided to MPLS connectioncontrol module 704 by PNNI routing module 706A. Routing module 706A hasknowledge of all paths, including all tunnels and the status of alltunnels. MPLS connection control module 708 then determines the newlabel information for first label 318 and second label 320 when sendingits appropriate data and CV frames out on connection 218. In connectioncontrol module 708, stack 720 comprising entries 722 of second labelfields is used to track primary and alternate MPLS routing paths. Thestack provides a pre-formed list of labels which can be used byconnection control module 704 allowing an efficient mechanism foridentifying new labels for alternate routes once it is determined thatthe current MPLS route is no longer viable.

It will be appreciated that the use of the MPLS CV OAM frames provides afault resolution of signals which should be received every second by theMPLS modules in switch 208. This compares favourably with the typicalPNNI signalling scheme which provides resolution of failures once every30 seconds and ATM signalling schemes which provides resolution ofinformation only once every 60 seconds.

Following is a description of exemplary interaction of the modules ofswitch 208 shown in FIG. 7 in the event of a failure in LSP 400. In CaseC of FIG. 6, switch 208 stops receiving CV frames. Accordingly, OAMstate machines 710 does not receive CV frames. After three consecutivemissed frames i.e., three seconds, state machines 710 determines thatthe LSP tunnel has failed. In response, state machine 710 sends an MPLSOAM CV Failure Detected Message to LSP management modules 714.

LSP management module 714 receives the Failure Detected Message andgenerates and sends a “link down” message to the ATM signalling system708.

The ATM signalling module 708 receives the “link down” message.Accordingly, each ATM connection that was previously using the failedlink now cannot pass data. The ATM signalling module 708 sends a “removeconnection” to MPLS connection control module 704 to remove the MPLSconnection. The ATM signalling module 708 marks the current failed LSPtunnel 400 as not being available for new ATM connections.

MPLS connection control module 704 receives the “remove connection”message. It programs the CV transmitter 602 to stop forwarding-frames tothe failed LSP tunnel 400 by changing the destination information inFirst Label Field 318 (FIG. 3).

If an alternate tunnel exists, such as tunnel 224, the ATM signallingmodule 708 reroutes the ATM connection across the other operational LSPtunnel. When the reroute is complete, ATM signalling module 708B sendsan “add connection” message to the MPLS connection control module 704 toenable the alternate tunnel 224 to be associated with the ATM traffic.

Following is a description of possible actions taken by switch 208 whenthe original failure is cleared and the OAM state machine 710 beginsreceiving CV frames. First OAM state machine 710 sends a “CV failurecleared” message to the LSP management module 714 by enqueing anappropriate message in FIFO 718. Next, LSP management module 714receives the “CV failure cleared” message and determines that thepreviously failed LSP is now operational. Accordingly it sends a “linkup” message to the ATM signalling module 706B. Finally, ATM signallingmodule 706B receives the “link up” message. It marks the previouslyfailed tunnel as now being available for new ATM connections. A furthersignal may be provided to connection control module 708 to re-use thepreviously failed tunnel.

It will be appreciated that from the prior art, it is not possible touse ATM OAM packets in MPLS OAM. Further, if an MPLS tunnel becomesnon-operational, no ATM signalling would have been notified of thefailure.

The foregoing embodiment has been described with a certain degree ofparticularity for the purposes of description. Those skilled in the artwill understand that numerous variations and modifications may be madeto the embodiments disclosed herein without departing from the scope ofthe invention.

1. A method of re-establishing a connection for a communication link,the communication link having a first portion in a first communicationnetwork, a second portion in a second communication network, and aninterface connecting the first portion to the second portion, the firstcommunication network having a first communication protocol and a firstoperation, administration, and maintenance (“OAM”) protocol adapted tomonitor integrity of the first portion, the second communication networkhaving a second communication protocol and a second OAM protocol adaptedto monitor integrity of the second portion, the method comprising:utilizing the second OAM protocol to detect a failure relating to alabel switched path (“LSP”) tunnel in the second portion by monitoringconnectivity verification (“CV”) frames of the second OAM protocol beingpassed over the LSP tunnel; upon detection of the failure, identifyingan alternate route for the second portion in the second communicationnetwork, the alternate route being able to complete the second portionof the communication link from the interface; and, for the communicationlink, at the interface replacing the second portion with the alternateroute.
 2. The method of claim 1 wherein the first and secondcommunication protocols are first and second network layer protocols,respectively.
 3. The method of claim 2 wherein the interface includes anadaptation function for the first and second communication networks. 4.The method of claim 3 wherein the first communication network is asource routed communication network.
 5. The method of claim 4 whereinthe first communication network is an asynchronous transfer mode (“ATM”)communication network.
 6. The method of claim 5 wherein the first OAMprotocol is one of a private network-to-network interface (“PNNI”)protocol and an ATM OAM protocol.
 7. The method of claim 6 wherein thesecond communication network is a multi-protocol label switching(“MPLS”) communication network.
 8. The method of claim 7 wherein thesecond OAM protocol is a MPLS OAM protocol.
 9. The method of claim 8wherein the identifying of the alternate route for the second portion inthe second communication network is performed at the interface.
 10. Themethod of claim 9 wherein the utilizing of the second OAM protocol todetect the failure in the second portion comprises monitoring the secondportion for receipt of frames containing OAM information and debouncingthe frames.
 11. The method of claim 10 wherein for the identifying ofthe alternate route for the second portion in the second communicationnetwork, a list of alternate routes for the second portion is maintainedand accessed to identify the alternate route.
 12. The method of claim 11wherein the first OAM protocol is adapted to detect failures in thesecond portion.
 13. The method of claim 10 and further comprising:utilizing the second OAM protocol to detect clearance of the failure inthe second portion; and, upon detection of the clearance of the failure,for the communication link, at the interface replacing the alternateroute with the second portion.
 14. A network node associated with afirst communication network and a second communication network, thenetwork node processing communications for a communication link having afirst portion in the first communication network, a second portion inthe second communication network, and an interface between the firstportion and the second portion at the network node, the firstcommunication network having a first communication protocol and a firstoperation, administration, and maintenance (“OAM”) protocol adapted tomonitor integrity of the first portion, the second communication networkhaving a second communication protocol and a second OAM protocol adaptedto monitor integrity of the second portion, the network node comprising:a first module adapted to detect a failure relating to a label switchedpath (“LSP”) tunnel in the second portion utilizing the second OAMprotocol by monitoring connectivity verification (“CV”) frames of thesecond OAM protocol being passed over the LSP tunnel; a second moduleadapted to receive an indication of the failure and upon receipt of theindication, to identify an alternate route for the second portion in thesecond communication network, the alternate route being able to completethe second portion of the communication link from the interface; and, athird module adapted to receive an indication of the alternate route andto replace the second portion with the alternate route for thecommunication link.
 15. The network node of claim 14 wherein the firstand second communication protocols are first and second network layerprotocols, respectively.
 16. The network node of claim 15 wherein theinterface includes an adaptation function for the first and secondcommunication networks.
 17. The network node of claim 16 wherein thefirst communication network is a source routed communication network.18. The network node of claim 17 wherein the first communication networkis an asynchronous transfer mode (“ATM”) communication network.
 19. Thenetwork node of claim 18 wherein the first OAM protocol is one of aprivate network-to-network interface (“PNNI”) protocol and an ATM OAMprotocol.
 20. The network node of claim 19 wherein the secondcommunication network is a multi-protocol label switching (“MPLS”)communication network
 21. The network node of claim 20 wherein thesecond OAM protocol is a MPLS OAM protocol.
 22. The network node ofclaim 21 wherein the first module utilizes the second OAM protocol todetect the failure in the second portion by monitoring the secondportion for receipt of frames containing OAM information and the firstmodule debounces the frames.
 23. The network node of claim 22 whereinthe second module further comprises a list of alternate routes for thesecond portion to identify the alternate route.
 24. The network node ofclaim 23 wherein: the first module is adapted to use the second OAMprotocol to detect clearance of the failure in the second portion; and,the third module is adapted to replace the alternate route with thesecond portion for the communication link upon detection of theclearance of the failure.